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‘Widespread methane leakage’ coming from hundreds of vents off East Coast ocean floor

Of all the global warming gasses, methane is one of the very worst. Pound for pound, the Environmental Protection Agency says its effect on global warming is 20 times greater than that of carbon dioxide. And though its lifetime in the atmosphere is substantially shorter than carbon dioxide, it’s “more efficient at trapping radiation.”

Now scientists have determined that 570 vents, called seeps, are leaking methane gas in the most unlikely of all places: the ocean floor just off the East Coast. The findings, published on Sunday in Nature Geoscience, suggest they’re emitting as much as 90 tons of greenhouse gasses every year and appear to debunk earlier belief that there were only three East Coast seeps beyond the continental shelf.

And if there are more of these seeps — a lot more — it could represent a previously unknown source of damaging carbon emissions.

“The discovery of widespread methane seepage on the northern U.S. Atlantic margin was indeed surprising,” lead author Adam Skarke of Mississippi State University wrote The Washington Post in an e-mail. “This is because [it] lacks the geological properties commonly known to be associated with widespread seafloor methane emissions.” It’s the first time, he said, that widespread leakage has been discovered in a non-Arctic location that’s both free of large gas reserve and substantial tectonic activity.

“Effects of these [methane] plumes on climate and ocean chemistry are not yet clear, but could extend well beyond the plumes themselves,” the journal Nature said in a press release.

The paper found that the vents, which are at depths from 800 to 2,000 feet, have a sprawling swath. They reach hundreds of miles from Cape Hatteras, N.C., to the Georges Bank southeast of Nantucket, Mass. “Widespread seepage hadn’t been expected,” the paper said.

The finding raises a number of questions. First on the list: Are there a lot more? The paper says the discovery suggests “tens of thousands” of similar vents could pockmark the ocean floor, emitting vast quantities of methane gas. He told the BBC that their number could be as high as 30,000.

If true, that would mean there is a significant — and heretofore unknown — addition to global carbon admissions, throwing previous estimates into question. “Such seeps would represent a source of global seabed methane emissions that have not been fully accounted for in previous carbon budgets,”
Worse, the seeps aren’t fresh ones. “The fact that it’s there in the quantities that it is — and [that] it is exposed — suggests that indeed the processes at these locations have been going on … at least 1,000 years,” Skarke told NBC News. He said he didn’t visit all the seeps, with the most concentrated clusters apparently located off the Chesapeake Bay, but “the ones we visited suggest a very prolonged seepage.”

There is one bit of good news: The depth of the East Coast seeps are so deep that the methane gas isn’t likely reaching the atmosphere. “The methane is dissolving into the ocean at depths of hundreds of meters and being oxidized into” carbon dioxide, Skarke told the BBC. “But it is important to say we simply don’t have any evidence in this paper to suggest that any carbon coming from these seeps is entering the atmosphere.”

It’s unclear from Skarke’s research the precise source of the methane gas. In most circumstances, seeps occur in areas of tectonic activity — like the West Coast — or in oil- or gas-rich basins, like the Gulf of Mexico. The East Coast isn’t known for its tectonic activity, but it’s possible deep reservoirs of gas are fueling some of the seeps, one researcher explained to the New York Times.

Meaning: The discovery could interest a few oil companies. But Skarke’s not buying the economic potential of the methane gas. “There is no evidence to say that [this is] related to conventional gas reservoirs,” he told the BBC. “So there is no evidence to say they are a recoverable resource.”